Generalized constraint collection management method

ABSTRACT

Techniques are provided to allow users of Electronic Design Automation (EDA) tools to define constraint template types for efficiently associating constraints with design objects to specify design intent. Processes for creating and validating the constraints are provided by user-defined plug-ins, thereby allowing users to annotate circuit designs with constraints for proprietary layout and fabrication processes without exposing the constraints to tool vendors or competitors. The constraints are re-created from the template types whenever the circuit design is loaded into the EDA tool, so that the constraints are based upon the latest version of the template type. The constraints are also re-created when validation fails. Constraint groups are reusable in different designs, technology nodes, and processes because they automatically expand to provide the specific constraints to achieve a goal. The specific constraints in a template type can be modified as technology changes, and the modification will automatically be applied to the design objects.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the design of electronic circuits and moreparticularly to association of constraints with design objects inelectronic circuit designs.

2. Description of the Related Art

Electronic Design Automation (EDA) tools are software programs that areused to design electronic circuits. A suite or combination of EDA toolsmay be used to convert a circuit design idea to a physical designincluding logic gates, circuit components, and their interconnections. Acircuit designer typically uses an EDA tool to create a schematic designof a circuit. The designer may use another EDA tool from the suite toconvert the schematic to a physical circuit layout, which includes theshapes, positions, and dimensions of semiconductor and conductormaterials such as silicon and metal. The EDA design tool in essencetranslates the schematic design to a physical layout using layout rules,which specify, for example, that a particular type of transistor is tohave particular dimensions and be a particular distance from othertransistors in the physical layout. The physical layout can befabricated to produce a physical implementation, which is typically asemiconductor chip.

The integrated circuit may be, for example, an analog circuit such as anamplifier, a digital circuit such as a microprocessor, or a combinationanalog and digital circuit, such as a cellular telephone radio. In oneapproach to circuit design, a designer creates the schematic diagram byadding design objects such as transistors, resistors, digital logicgates, and other devices to a design canvas. The designer connects thedesign objects using connections that are represented as lines in theschematic.

A design canvas is typically a two-dimensional area displayed by the EDAtool. The EDA tool may provide a user interface to allow the designer tomodify the schematic design by modifying existing design objects on thecanvas, by adding new design objects to the canvas, and by modifying oradding connections between the objects on the canvas. Some prior customdesign tools allow the designer to produce “custom designs” by providinga selection of design objects that can be placed at locations on thecanvas specified by the designer. Locations on the canvas may correspondto locations on the physical material on which the circuit is to befabricated, thereby allowing the designer to control the placement ofphysical devices on the physical circuit.

Often, design annotations are used to communicate design intent amongdesigners, and to archive design intent. A design annotation may includeone or more data values such as parameter values for layout rules. Thedata values may be, for example, text in a format that is readable byhumans or machines. A design annotation may also include one or morenames associated with the data values, e.g., to identify specificparameters to which the data values correspond. Design annotations aretypically created by a user via an EDA tool user interface or by aprogrammatic script, and are typically associated with particular designobjects.

Annotations that can be recognized and used by the design tool orfabrication process are called “constraints”. Constraint-driven designis a state-of-the-art technique for productivity enhancement in moderndesign automation software. A constraint is typically identified by aname, which is associated with an optional value, which may specifydetails about the constraint. A constraint can be attached to one ormore design objects, typically by a designer who wishes to specifyinformation about a design object for the purpose of, for example,overriding default layout parameters provided by the base EDA tool, orfor providing additional layout or process parameters not provided bythe base EDA tool. For example, a symmetry constraint may specify thattwo devices are to be positioned symmetrically in the physical layout.An orientation constraint may specify that a device is to be positionedwith a particular orientation, where the orientation is specified by thevalue of the constraint. The design tool may recognize and act on theconstraints when generating the layout. The constraint may also be usedin the fabrication process when fabricating the physical circuit.

Designers typically enter constraints for a circuit into one or more EDAtools as part of the process of designing the circuit. However, as moreconstraint-driven algorithms become available, there is a correspondingincrease in the number, complexity, and specialization of constraintsthat are available to the designer. Unfortunately, the designer'sproductivity can be impeded by time spent selecting and entering theappropriate constraints. Automated constraint entry techniques such asscripts and hard-coded entry of constraint groups have been developed toaddress this productivity impediment. Scripts have been used to generatethe constraints automatically, e.g., by generating multiple constraintsin response to one user action. However, the scripts often fail toaccommodate continuous incremental changes to the constraints. Changesordinarily must be made to the scripts over time in response to changesin the underlying technology that implements the circuit. Unfortunately,using existing change methodologies to change scripts can beerror-prone, because, for example, an operator may enter incorrectconstraints, or a script that generates constraints may contain an errorthat may introduce incorrect or inconsistent constraints.

Hard-coded entry of groups of constraints is another technique meant toaddress the productivity impediment. With this group-based approach,multiple constraints can be entered at once, e.g., in response to oneuser action, so the constraint entry process is somewhat simplified, butsuch techniques still require restarting the constraint entry task fromscratch for new technology or new constraint driven tools and are,therefore, subject to technological obsolescence.

Users of the EDA tool may define constraints and associated instructionsfor creating the constraints, such as scripts or constraint groups. Suchuser-defined constraints are typically used by user-defined tools thatinteract with the EDA tool, such as tools for generating physicalcircuit layouts and tools for controlling the chip fabrication process.Different designs and different users may employ different specializedconstraints to achieve design goals. The goals and the constraints usedto achieve them may be proprietary. Therefore, there is a benefit topermitting users to define customized, specialized constraints withoutrevealing such constraints to other parties, such as the EDA toolvendor, for example. Therefore, the constraints, associatedinstructions, and circuit designs that use the constraints should notordinarily be accessible by other users, or by the EDA tool vendor, forexample.

There has been a need for techniques of automatically creatingconstraints for a circuit design in an EDA tool while maintainingcorrectness of the constraints over time, e.g., as technology, thecircuit design, and the EDA tool change. There also has been a need toenable users to extend the EDA tool to allow the tool to create andmaintain constraints according to user-defined instructions. There hasfurther been a need to allow users to protect their extensions, andcircuit designs that use their extensions, from unauthorized use byother users. Therefore, it would be desirable to have a technique forautomatic management of constraints that accommodates changes to theconstraints and changes to the tools, and permits easy development ofcustomized constraints while minimizing the risk of revealingproprietary information.

SUMMARY OF THE INVENTION

In general, in a first aspect, the invention features a method ofautomating the application of constraints to design objects in a circuitdesign created using an electronic design automation tool. The methodcomprises receiving selection of a circuit design object that representsa physical circuit object in a circuit being designed in the electronicdesign automation tool, receiving selection of a template type thatproduces a constraint that represents a physical limitation uponimplementation of the circuit design object in the circuit, wherein thetemplate type is represented in the electronic design automation tool bya selectable user interface feature, and producing a template instancebased upon the template type, wherein the template instance associatesthe constraint with the circuit design object to represent in theelectronic design automation tool that the physical limitation of theconstraint applies to the circuit design object.

Embodiments of the invention may include one or more of the followingfeatures. Producing the template instance may include identifying atemplate instance generation process associated with the template type,invoking the generation process to create the template instance, andassociating the circuit design object with the template instance. Thetemplate instance generation process may be provided by a user of thedesign automation tool. The method of automating the application ofconstraints may further comprise providing the design object and atemplate instance parameter to the template instance generation process.The template instance generation process may comprise creating theconstraint; associating the parameter with the constraint, andassociating the design object with the constraint.

The circuit design object may be stored in a circuit design file,wherein a representation of the template instance is stored to thecircuit design file, and wherein the representation includes an instancename, a template type identifier that specifies the template instance'stype, and a design object identifier that specifies the design object.The design automation tool may be stored in at least one tool fileprovided by a design automation tool vendor and the template instance'stype may be stored in a template type plug-in file, wherein the at leastone tool file, the template type plug-in file, and the circuit designfile are separate files. The template instance may include a templateinstance parameter, and the method of automating the application ofconstraints may further comprise storing in the circuit design file thetemplate instance parameter, wherein the instance parameter isassociated on the storage medium with the template instance.

The template instance may include at least one constraint, and the atleast one constraint may include a constraint parameter, and the methodof automating the application of constraints may further comprisestoring in the circuit design file the at least one constraint, whereinthe at least one constraint is associated in the circuit design filewith the template instance. The circuit design may include a pluralityof design objects, the at least one constraint may include a referenceto at least one of the design objects, and the method of automating theapplication of constraints may further comprise storing in the circuitdesign file the reference, wherein the reference is associated in thecircuit design file with the individual constraint.

In general, in a second aspect, the invention features a method ofautomating the validation of constraints associated with circuit designobjects in a circuit design created using an electronic designautomation tool. The method of automating validation comprises receivingnotification of a change action that affects the design, identifying atemplate instance validation process associated with the template type,invoking the validation process to validate the constraints, receiving avalidity indicator from the validation process, and if the validityindicator indicates that the constraints are not valid, invoking arecovery process.

Embodiments of the invention may include one or more of the followingfeatures. The method of automating validation may further compriseretrieving the template instance validation process from a plug-in fileassociated with the template type. The template instance validationprocess may be provided by a user of the design automation tool. Themethod of automating validation may further comprise providing the atleast one design object and a template instance parameter to thetemplate instance validation process. The template instance validationprocess may comprise determining if the value of at least one constraintparameter associated with at least one of the constraints is valid; ifthe constraint parameter is valid, generating a success indicator; andif the constraint parameter is not valid, generating a failureindicator. The recovery process may comprise deleting the constraints,identifying a template instance generation process associated with thetemplate type, and invoking the template instance generation process tore-create the constraints.

The change action may comprise reading in of a template instance from astorage medium, modification of a template instance parameter, or acombination thereof. The change action may comprise modification of thecircuit design. The change action may comprise a change to the at leastone constraint, and the recovery process may comprise rejecting thechange action. The method of automating the application of constraintsmay include displaying a template instance representation correspondingto the template instance. The method of automating the application ofconstraints may further include displaying a template instance treecomprising a template instance node, wherein the template instance noderepresents the template instance. The method of automating theapplication of constraints may further include displaying a constraintnode as a descendant of the template instance node in the templateinstance tree, wherein the constraint node represents a constraintassociated with the template instance, and displaying a design objectnode in the tree as a descendant of the constraint node, wherein thedesign object node represents the design object.

In general, in a third aspect, the invention features a system forautomating the application of constraints to design objects in a circuitdesign created using an electronic design automation tool. The systemcomprises a design object selector to receive selection of a circuitdesign object that represents a physical circuit object in a circuitbeing designed in the electronic design automation tool, a template typeselector to receive selection of a template type that produces aconstraint that represents a physical limitation upon implementation ofthe circuit design object in the circuit, wherein the template type isrepresented in the electronic design automation tool by a selectableuser interface feature; and a template instance producer to produce atemplate instance based upon the template type, wherein the templateinstance associates the constraint with the circuit design object torepresent in the electronic design automation tool that the physicallimitation of the constraint applies to the circuit design object.

Embodiments of the invention may include one or more of the followingfeatures. The system may comprise a process selector to identify atemplate instance generation process associated with the template type,a process invoker to invoke the generation process to create thetemplate instance, and an associator to associate the circuit designobject with the template instance. The system may comprise a designobject writer to store a design object of the circuit design to thecircuit design file, and a template instance writer to store arepresentation of the template instance to the circuit design file,wherein the representation includes an instance name, a template typeidentifier that specifies the template instance's type, and a designobject identifier that specifies the design object.

In general, in a fourth aspect, the invention features a system forretrieving a circuit design annotated with a constraint from a circuitdesign file on a persistent storage medium. The system comprises atemplate instance reader to retrieve a representation of a templateinstance from the circuit design file, wherein the representationincludes an instance name, a template type identifier, and at least onedesign object identifier; a template type selector to identify atemplate type specified by the template type identifier, a generatorplug-in locator to identify a template instance generator associatedwith the template type if the template type is accessible, and agenerator plug-in invoker to invoke the template instance generator tocreate a restored template instance if the instance generator isaccessible, wherein the restored template instance includes a constraintthat references at least one design object, wherein the at least onedesign object is specified by the at least one design object identifier.

In general, in a fifth aspect, the invention features a system forproviding a constraint manager user interface in an electronic designautomation tool. The system comprises a template instance generator tocreate a template instance in response to selection of a template typebutton, wherein the template instance is an instance of a template typeassociated with the button, a design object selector to receiveselection of a design object, a design object mapping component toassociate the design object with the template instance, and a templateinstance display component to display a template instance treecomprising a template instance node, wherein template instance noderepresents the template instance.

In general, in a sixth aspect, the invention features a computer programproduct comprising program code for automating the application ofconstraints to design objects in a circuit design created using anelectronic design automation tool. The computer program productcomprises program code operable to receive selection of a circuit designobject that represents a physical circuit object in a circuit beingdesigned in the electronic design automation tool, program code operableto receive selection of a template type that produces a constraint thatrepresents a physical limitation upon implementation of the circuitdesign object in the circuit, wherein the template type is representedin the electronic design automation tool by a selectable user interfacefeature, and program code operable to produce a template instance basedupon the template type, wherein the template instance associates theconstraint with the circuit design object to represent in the electronicdesign automation tool that the physical limitation of the constraintapplies to the circuit design object.

In general, in a seventh aspect, the invention features a computerprogram product comprising program code for automating the validation ofconstraints associated with design objects in a design created using anelectronic design automation tool. The computer program productcomprises program code operable to receive notification of an changeaction that affects the design, program code operable to receiveidentify a template instance validation process associated with thetemplate type, program code operable to receive invoke the validationprocess to validate the constraints, program code operable to receivinga validity indicator from the validation process, and program codeoperable to invoke a recovery process if the validity indicatorindicates that the constraints are not valid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an illustrative drawing of a constraint manager and relatedcomponents in accordance with some embodiments of the invention.

FIG. 1B is a schematic drawing of an illustrative computer system 10that can run novel processes for generating and validating constraintsin accordance with embodiments of the invention.

FIG. 2 is an illustrative drawing of prior art constraints in anElectronic Design Automation tool.

FIG. 3A is an illustrative drawing of a constraint manager userinterface in an Electronic Design Automation tool in accordance withsome embodiments of the invention.

FIG. 3B is an illustrative drawing of a constraint manager userinterface displaying specific constraints in an Electronic DesignAutomation tool in accordance with some embodiments of the invention.

FIG. 4 is an illustrative drawing of a process for generating a templateinstance in accordance with some embodiments of the invention.

FIG. 5 is an illustrative drawing of a process for validating a templateinstance in accordance with some embodiments of the invention.

FIG. 6 is an illustrative drawing of a process for validating a templateinstance in accordance with some embodiments of the invention.

FIG. 7, is an illustrative drawing of a process for defining a templatetype in accordance with some embodiments of the invention.

FIG. 8 is an illustrative drawing of a process for creating a templateinstance in an Electronic Design Automation tool user interface inaccordance with some embodiments of the invention.

FIG. 9 is an illustrative drawing of a template instance generationsub-process in accordance with some embodiments of the invention.

FIG. 10 is an illustrative drawing of a template instance validationsub-process in accordance with some embodiments of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofparticular applications and their requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Moreover, in the following description, numerousdetails are set forth for the purpose of explanation. However, one ofordinary skill in the art will realize that the invention might bepracticed without the use of these specific details. In other instances,well-known structures and devices are shown in block diagram form inorder not to obscure the description of the invention with unnecessarydetail. Thus, the present invention is not intended to be limited to theembodiments shown, but is to be accorded the widest scope consistentwith the principles and features disclosed herein.

FIG. 1A is an illustrative drawing of a constraint manager and relatedcomponents in accordance with some embodiments of the invention. An EDAtool 100 allows a user 101 to create a circuit design 102 thatrepresents an electronic circuit. The circuit design 102 is typically adata structure in a computer-readable memory. The user 101 may be, forexample, a human user of the EDA tool. The user 101 is typicallyassociated with an organization such as a chip design company. The EDAtool 101 is typically provided by an organization such as an EDA toolvendor. The circuit design 102 includes a set of design objects 103which represent devices, connections, and other features in theelectronic circuit. The design objects 103 include at least one designobject, shown as Design Object A 104, also referred to herein as adesign object 104. The user 101 interacts with the EDA tool 100 via auser interface 105. The EDA tool 100 may be, for example, the CadenceVirtuoso™ Custom Design Platform from Cadence Design Systems of SanJose, Calif., or another tool for creating circuit designs.

Each design object, such as the design object 104 may be associated withone or more constraints 133, as illustrated by the arrows from theconstraints 133 to the design objects 103. The arrows are exemplary andrepresent one possible set of associations; other associations, i.e.,relations or arrows, are possible between the design objects 103 and theconstraints 133. The particular set of associations is established bythe user 101 for a particular circuit design 102. In general, each ofthe deign objects 103 may be associated with zero or more of theconstraints 133, and each of the constraints 133 may be associated withzero or more of the design objects 103.

The design object 104 may be, for example, a data structure stored in acomputer-readable memory. As described above, the constraints 133represent design intent, i.e., goals, for the design object 104, e.g.,desired properties of the design object. The constraints 133 may be usedby other portions of the EDA tool or by other EDA tools, such as alayout tool or a placement and routing tool (not shown), which maydetermine a position or orientation of the device based upon theconstraints, or in fabrication of a physical device or featurerepresented by the design object 104, where parameters of thefabrication process may be based upon the constraints 133. A constraintmay be, for example, a minimum or maximum distance between two designobjects, or an orientation between two design objects. Examples oftypical constraint types are shown in the table below.

Constraint Types Constraint Type Description Symmetry Specifies adesired symmetry relation between design objects. Correlation Specifiesa desired correlation between design objects. matchedParametersSpecifies a desired parameter matching between design objects.Orientation Specifies a desired orientation relationship between designobjects. Alignment Specifies a desired alignment relationship betweendesign objects. layoutStructure Specifies a desired layout structure fordesign objects. Cluster Specifies a desired cluster relationship betweendesign objects. parasiticEstimate Specifies an estimated parasitic valuefor design objects. parasiticFilter Specifies a desired parasitic filterfor design objects. areaUtilization Specifies a desired area utilizationfor design objects. boundaryArea Specifies a desired boundary area fordesign objects. Distance Specifies a desired distance between designobjects. powerStructure Specifies a desired power structure for designobjects. IRDrop Specifies a desired voltage drop between design objects.relativeOrientation Specifies a relative orientation between designobjects.

A template manager 120 interacts with a set of user-defined templatetypes 150 to manage, i.e., create and verify, using user-definedinstructions, sets of constraints associated with the design objects103. Each set of constraints 133 may, for example, represent one or moredesign goals or designer-specified parameters for the design objects103. For example, the constraints 133 may specify that placement of aspecified set of design objects in a particular orientation or within aparticular distance is desired.

The constraint manager produces a technical effect by assigningconstraints to circuit design objects and enforcing the validity of theconstraints in an electronic circuit design representation in anElectronic Design Automation tool. The constraints produce a technicaleffect by, for example, affecting the process of manufacturing aphysical semiconductor chip by providing parameter values for steps inthe chip layout or fabrication processes. In one aspect, the constraintmanager improves the efficiency of the process of assigning constraintsto circuit designs by providing features that a circuit designer can useto group constraints. The constraint manager thereby simplifies the taskof assigning multiple constraints to a design object.

A template type 151 includes a template instance generation process 152and a template instance validation process 154 to, respectively, createand verify groups of constraints. Note that the processes describedherein may be implemented as a subroutine that includes instructionsexecutable by a computer.

The processes 152,154 and other portions of the constraint template type151 may be packaged, i.e., stored as a plug-in. A plug-in may be storedin a file, and may include files and associated instructions forregistering the processes 152,154 with the template manager 120 so thatthe template manager 120 can invoke the processes. For example, theprocesses 152,154 may be registered with the template manager 120through commands in an application command interface of the EDA tool100. These commands can be typed interactively by the user 101 orinvoked automatically. e.g., by a startup script that is invoked whenthe EDA tool 100 is initialized. The plug-in may include implementationsof the processes 152,154 for each template type in a set of user-definedtemplate types. Template types may also be provided by the EDA toolvendor. Such vendor-provided template types may be used as-is by theuser 101, or may be customized or extended by the user to reflectspecific aspects of users' circuit design technology.

The constraints 133 are associated with or contained in a templateinstance 132. The template instance 132 may be represented as, forexample, a set of data values or an object instance stored in a computermemory. Each template instance 132 may include a reference to thetemplate type 151 that was used to create the template instance, asshown by the arrow from the template instance 132 to the template type151. Multiple different template instances may be created for eachtemplate type 151, and each template instance 132 may include acorresponding set of constraints 133.

Each template instance 132 includes an instance name 134 which may be,for example, a text string that describes the template instance. Eachtemplate instance 132 may also include one or more template instanceparameters 135. The template instance parameters 135 allow the user 101to specify per-template-instance values that may be accessed by thetemplate instance validation process 154. The user may specify thevalues for the template instance parameters via, for example, theparameter list user interface feature 348 of FIG. 3A.

In one sense, the template instance 132 can be understood as a containerthat allows the EDA tool, and therefore the user 101, to treat the setof constraints as a single entity with a name and a type. The templateinstance can be manipulated, e.g., created, modified, and deleted, byuser interface actions that apply to the constraints in the templateinstance, so the user 101 can more easily manage multi-constraintexpressions of design intent. Furthermore, because the template instancehas an associated type, changes to the set of constraints associatedwith a particular type of design intent, or changes to creation orvalidation behavior associated with the type of design intent, can bemade in a single place, i.e., the template type, and may beautomatically propagated to existing constraints contained in templateinstances, as well as to constraints in subsequently-created templateinstances. The template type's validation process 154 ensures thatchanges made to the constraints do not result in an invalid constraintset 133. The validation process 154 ensures that the constraint set 133remains valid by re-creating the constraint set 133 if validation fails,and, if the constraint set 133 cannot be re-created in a valid state, byrejecting the changes.

A constraint 136 in the set of constraints 133 may refer to one or moredesign objects 103 to represent design goals for the design objects 103.The individual constraints in the set of constraints 133 defined by atemplate type may be related or unrelated to each other, but typicallyare related to a particular design goal represented by the templatetype, such as placement of a specified set of design objects in aparticular orientation or within a particular distance. Each of theconstraints 133 may be associated with one or more constraint parameters137, which can be name-value pairs which represent the actual designannotations that the constraint 133 applies to the design objects 103.

Each of the constraints 133, e.g., Constraint A 136, may be applied toone or more of the design objects 103 by establishing an associationbetween the constraint 136 and the design objects 103. In oneembodiment, each of the constraints 133 includes a reference, i.e., alink, to one or more of the design objects 103 with which the constraintis associated. FIG. 1A shows examples of possible associations betweenthe constraints 133 and the design objects 103. Constraint A 136 isassociated with Design Object A 104 and Design Object B 106, as shown bythe arrow 161 from Constraint A 136 to Design Object A 104 and the arrow162 from Constraint A 136 to Design Object B 106, respectively. In oneaspect, Constraint A 136 is a constraint that relates the two associateddesign objects 104,106, such as a distance constraint that specifies acertain distance, specified by constraint parameters 137, to bemaintained between the two design objects 104,106.

Similarly, Constraint B 138 is associated with Design Object B 108,Design Object C 110, and Design Object X 114, as shown by the arrowsfrom constraint B 138 to the respective design objects. Constraint B 138may be, for example, an alignment constraint that specifies how theassociated design objects are to be aligned relative to each other, inwhich case Constraint parameters 139 of Constraint B 138 would specify atype of alignment, e.g., edge, to indicate that the edges of theassociated design objects should be aligned.

Constraint X 140 may be, for example, an IR Drop constraint, whichspecifies a desired voltage drop for the associated Design Object C 110,in which case constraint parameters 141 of Constraint X 140 specify thevalue of the desired voltage drop.

In FIG. 1, the association between design objects and constraints isrepresented as arrows from constraints 133 to design objects 103. Forexample, the arrows 161,162 represent the association of the DesignObject A 104 and the Design Object B 108 with the Constraint A 136, asdescribed above. These arrows may be implemented in a computer programas, for example, pointers or object references stored in the constraints133, where the pointers or object references point to or refer to thedesign objects 103 associated with the constraints 133.

The association between design objects and constraints may berepresented in other ways, e.g., as a list of design objects andassociated constraints, or as reference links in the design objects,where the reference links refer to constraints.

The template manager 120 creates the template instances 130, which mayinclude template instance objects that are instances of template typesin the list of template types 150. The template instances 130 may be,for example, data structures or objects stored in a computer readablememory. For illustrative purposes, three template instances are shown,including a Template Instance A 132, a Template Instance B 132, and aTemplate Instance X 144. Each of the template instances 130 is createdby and associated with the design object 104 by the template manager120. For example, in response to a user-initiated command to create atemplate instance, a template instance generator 122 of the templatemanager 120 invokes a user-defined template instance generation process152 to create a template instance 132 and create a set of constraints133 of the template instance 132. The set of constraints 133 is createdby the template instance generation process 152.

The template manager 120 also causes the template instances 130 to bevalidated when appropriate. For example, in response to modification ofat least one of the design object references 161 associated with aconstraint 136, or in response to modification of name-value pairparameters associated with the template instance 132 or with theconstraint 136, or in response to reading in of a template instance froma file, a template instance validator 124 of the template manager 120invokes a user-defined template instance validation process 154 tovalidate the template instance 132.

The template manager 120, including the template instance generator 122,which may be a process, and the template instance validator 124, whichmay also be a process, may be implemented in a computer program encodedin computer readable media. For example, the template manager 120 may beimplemented in a programming language such as Cadence® SKILL, Lisp, C++,Java™ or the like.

The template instances 130 can be created when a user 101 interacts withthe user interface 105 by selecting a particular template type 151 to beassociated with one or more user-selected design objects 103. Thetemplate instance 132 maintains a link, i.e., a reference, to thetemplate type 151 from which the template instance 132 was created. Thislink provides for updating of the template instance 132 over time astechnology changes. For example, if the technology underlying theconstraints for a goal associated with the template type 152 changes,then the template instance 132 may be re-created with the newconstraints. The template instance validation process 154 may initiatesuch a re-creation by examining the template instance 132 to determineif the template instance includes appropriate, e.g., up-to-date,constraints 133. The template instance generation process 142 and thetemplate instance validation process 154 may be modified over time tocause re-creation of template instances and constraints to reflectchanges in technology. Automatic creation of constraints whilemaintaining constraints in a correct-by-construction manner is providedby the constraint manager and user-defined template instance generationand validation sub-processes, which the user can define to providetechnology-specific constraints and validation behavior. The user canextend the features of the EDA tool with template types that providethose automatic constraint creation and correctness preservationfeatures.

The constraint manager can improve design and manufacturing efficiencyby detecting and correcting invalid, i.e., inconsistent, constraints orconstraint groups. Invalid constraints may result in fabrication ofdefective chips, or, if the invalid constraints are detected at a laterstage, in wasted effort, because errors detected later in the chipmanufacturing process are more difficult to correct than errors detectedearlier, such as during the design phase.

When the template instance 132 is associated with a design object, suchas the design object 104, the constraints 133 in the template instanceare automatically applied to (i.e., associated with) that design objectfor subsequent use by other portions of the EDA tool 100. Multipletemplate instances 130 may be created from a single template type 151.The constraints 133 in a template instance 132 are generated by auser-defined instance generation process 152 of the template type 151.The instance generation process 152 may be packaged as a plug-in, and isinvoked by a template manager 120 when a user requests creation of a newtemplate instance for that type. The template manager 120 includes atemplate instance generator 122, which calls the instance generationprocess 152 to create the template instance 132.

The user 101 may associate template instances 130 with design objects103 by interacting with the user interface 105. The template instance132 may include multiple constraints, as illustrated by a Constraint A136, a Constraint B 138, and a Constraint X 140. Each constraintincludes a set of one or more constraint parameters 137, which are, forexample, name-value pairs. In one aspect, the name of a constraintparameter 137 represents a required or desired property of the circuitdesign, and the associated value represents the value of that property.

After the template instance 132 has been associated with one or more ofthe design objects 103 by the user 101, the integrity, i.e.,correctness, of the constraints 133 in the template instance, may bevalidated in response to certain events. The constraints 133 arevalidated because the constraints can be modified or deleted by, andsuch modification or deletion can lead to an incorrect or incomplete setof constraints 133. This validation of the constraints 133 is performedby a user-defined instance validation process 154 associated with thetemplate type. The instance validation process may be packaged as aplug-in, and is called by the template manager in response to certainevents. These events include reading a template instance from a storagemedium such as a disk file, modification of a template instanceparameter, or modification of a constraint. A template instanceparameter allows a user 101 to specify a value to be associated with atemplate instance. These modifications may be performed, for example, bythe user. When any of those events occur, a template instance validator124 of the template manager 120 invokes the instance validation process154. The instance validation process 154 checks the constraints 133 andany other content of the template instance 132 using conditions definedby the user. If the template instance validation process 154 finds thatthe template instance 132 is valid, then the template instance validator124 takes no further action. However, if the template instance is foundto be invalid, then the template instance validator 124 may replace theexisting constraints 133 with a newly-created set of constraints, ordelete the template instance, or reject the change, depending on thetype of event.

A process or sub-process is a set of computer program code instructionsthat can be invoked, i.e., called, by other computer program codeinstructions, which are referred to herein as invokers. The instructionsin a process are executed when the process is invoked. Parameter passingmay occur, i.e., input objects may be passed from the invoker to theprocess when the process is invoked, and output objects may be passedfrom the process to the invoker when the process returns, i.e. finishesexecuting or executes a return statement. The process may have processarguments, which are names and types of objects accepted by the process.The arguments receive particular objects provided by the invoker whenthe process is invoked. The objects provided by the invoker are referredto as parameters. The process may use the parameter objects passed bythe invoker to perform computations, and may compute one or more outputvalues, which are returned to the invoker when the process returns.

For example, a user-defined process may be invoked by an EDA tool at aparticular point in the EDA tool's execution. Such a user-definedprocess, which is referred to as a plug-in, allows the EDA tool to beextended with user-defined behavior so that users such as the user 101can customize the EDA tool for use with their design, layout, andfabrication processes.

In one aspect, the processes 152,154 are associated with each instanceof the template type 151. Invoking the template instance generationprocess 152 twice with the same input, i.e., with the same parametersand design objects, will produce two with the same constraints 133.Invoking the template instance validation process 154 on two templateinstances of the same template type 151 with the same parameters anddesign objects will produce the same result, i.e., valid or invalid.

FIG. 1B is a schematic drawing of an illustrative computer system 10that can run novel processes for generating and validating constraintsin accordance with embodiments of the invention. The computer system 10includes one or more central processing units (CPU's) 12, a userinterface 14, computer readable storage media 16, a system bus 18, andone or more bus interfaces for connecting the CPU, user interface,memory and system bus together. The computer system also includes anetwork interface 20 for communicating with other devices 22 on acomputer network.

Computer-readable code such as code for implementing the templateinstance generation process of FIG. 4, the template instance validationprocess of FIG. 5 or FIG. 6, the template instance generationsub-process of FIG. 9, or the template instance validation sub-processof FIG. 10 can be stored in the storage memory 16 and used to controlthe CPU 12. Moreover, a data structure representing constraint templateinstances such as the template instance data structures 130 can bestored in storage memory 16. The computer program instructions can causethe CPU 12 to produce the template instance data structures 130 and togenerate and validate constraint templates that associate constraintswith the design objects 103 of the circuit design 102.

FIG. 2 is an illustrative drawing of prior art constraints in anElectronic Design Automation tool. An EDA tool user interface 200 isprovided by an EDA tool (not shown). The user interface 200 is displayedon, for example, a workstation computer, and interacts with a user 201,who is typically a circuit designer. The user interface 200 provides adesign canvas 202. The design canvas 202 is an area upon which designobjects can be placed, positioned, and connected. The user 201 interactswith the user interface 200 to place representations of design objects,such as a transistor representation P1 204 and a transistorrepresentation N2 206, on the design canvas 202 to create a circuitdiagram 203, which is a displayed representation of a circuit designcorresponding to the circuit design 102 of FIG. 1A.

The EDA tool typically stores the circuit diagram 203, including thedesign objects on the design canvas 202, on a storage medium such as adisk file. The EDA tool can subsequently read in the circuit diagram 203from the file, so that the circuit diagram can persist after the EDAtool program has stopped running, or after the workstation has lostpower. The file also allows the circuit diagram 203 to be shared amongdifferent users in different locations. The file may be stored on astorage medium such as a magnetic disk or tape. Users' intellectualproperty is typically encoded in constraint management and validationsub-processes. Such intellectual property is protected from unauthorizeddistribution because users need not make their template types orsub-processes public. In one aspect, users can control the distributionof circuit designs that use their constraint types because the templateinstances, i.e., constraints, associated with circuit designs can onlybe loaded by the EDA tool if the template types and sub-processes areavailable. That is, loading of a template instance is prevented if thetemplate instance's corresponding template type definition is notavailable to the EDA tool.

The user 201 may add design objects such as the transistor P1 204 to thecircuit design 203, e.g., by selecting a transistor device from apalette of device types (not shown) and placing the transistor device atan appropriate position on the canvas 202. The user 201 may connect thedesign objects using connectors, which are another type of designobject. The user may associate constraints with the design objects ofthe circuit design 203 by, for example, selecting a design object fromthe palette, selecting a menu option to add a constraint, and enteringthe name and value of the constraint. In this example, a constraintbrowser 208 shows two constraints, an orientation constraint 210 and adistance constraint 218. The orientation constraint 210 indicates, e.g.,to a circuit designer or to another component of the EDA tool, thatassociated design objects 216 should be oriented in a certain way, asspecified by parameters 214. The orientation constraint 210 isassociated with the transistor P1 204 and the transistor N1 206, asshown by the associated design objects 216. The distance constraint 218is similarly associated with the transistor P1 204 and the transistor N1206, as shown by associated design objects 224. The distance constraint218 indicates that the associated design objects 224 should be separatedby a distance specified by a distance parameter 222.

FIG. 3A is an illustrative drawing of a constraint manager userinterface in an Electronic Design Automation (EDA) tool in accordancewith some embodiments of the invention. An EDA tool user interface 300includes a design canvas component 302 similar to the design canvas 202described above. The EDA tool user interface is an example of the userinterface 105 of FIG. 1A. The EDA tool user interface 300 also includesa constraint manager component 303, which is a user interface thatdisplays a set of template types 310 and allows a user to create atemplate instance 326.

A user may associate constraints with design objects by creating atemplate instance. To create a template instance, the user identifiesthe design objects that are to be constrained, e.g., by selecting one ormore design objects, such as the transistors 304,306, from the designcanvas 302. Next, the user selects a template type from a set oftemplate types 310 to create the desired constraints. The set oftemplate types 310 is shown as a set of icons, which are user interfacefeatures that have a distinct visual appearance. Two example templatetype icons, icon T 312 and icon U 314, are shown. The template types312,314 are displayed as icons that include illustrations of, forexample, a single-letter abbreviation that identifies the template type.Alternatively, the template types could be displayed as a menu of typenames, e.g., a drop-down or pop-up menu. The name or icon 312 of thetemplate type typically indicates the goal associated with the templatetype, to allow the user to decide, based on the appearance of the nameor icon, which template type to select to create a desired set ofconstraints.

Next, the user may provide values for template instance parameters. Thenames and types of template instance parameters are provided by thetemplate type and may be displayed as data fields for which the user canprovide values. A template instance is then created by the templatemanager 120 of FIG. 1A. The template instance includes the constraintsfrom and stores references, i.e., links, to the design objects and thetemplate instance parameters. For example, the design object 334 mayrepresent the transistor 304, and the design object N 336 may representthe transistor 306.

The constraint manager 303 displays previously-created independentconstraints, such as an independent constraint 322, andpreviously-created template instances, such as the template instance 326and a template instance N 346. The independent constraint 322 is aconstraint that is not associated with a template instance and isordinarily created directly, i.e., without use of a template instance,in response to a user command. The independent constraint 322 may beassociated with independent constraint parameters 324. When a newindependent constraint or template instance is created, a visualrepresentation of the constraint or template instance is displayed bythe constraint manager 303 with the existing constraints and templateinstances, e.g., below those existing objects in a scrollable list.

Each displayed template instance may be shown in an expanded state or ina collapsed state. The template instance 326 is shown in the expandedstate, in which a template instance name 328, constraints 332, designobjects 334,336, and constraint parameters 333 are displayed. Thetemplate instance N 346 is shown in the collapsed state, in which onlythe template instance name is shown. The user can toggle between theexpanded and collapsed states by selecting a tree expansion userinterface feature 321, which is displayed, for example, as a boxenclosing an arrow adjacent to the object, e.g., template instance orconstraint, which can be expanded or collapsed.

The template instance 326 is shown in the expanded state, with anassociated constraint 330 and an associated constraint N 338. Theconstraint 330 is also shown in the expanded state, in which constraintparameters 333, a design object 334, and a design object N 336 areshown. The constraint parameters 333 have initial values, which areprovided by the template type 312. The values of the constraintparameters 333 may be changed by the user.

The user may provide template instance parameter values in the parameterlist user interface feature 348, which may be, for example, a two-columnlist 350, in which the first column displays a parameter name 352, andthe second column displays a parameter value 354. The user may edit theparameter value 354 to change the value of a parameter. The parameterlist feature 348 displays the predefined template type parameters. Theuser may select parameter values for the template instance using a dropdown menu or similar user interface feature (not shown). In one example,the template instance 326 displays template instance parameters but notconstraint parameters. In another example, the same parameters, e.g.,both the template instance parameters and the constraint parameters, maybe displayed as part of both the template instance 326 and the parameterlist feature 348. The template instance 326 appears in the EDA tool userinterface 300 as a displayed representation of the template instance.

FIG. 3B is an illustrative drawing of a constraint manager userinterface displaying specific constraints in an Electronic DesignAutomation tool in accordance with some embodiments of the invention.Specific constraints are shown in the EDA tool user interface 300,including an independent Symmetry constraint 362 with an associatedconstraint parameter 364 that has the value “Mirror”. A templateinstance 326 is named “Match”, as shown by the name 368. The Matchtemplate instance 326 includes a Distance constraint 370, an Alignmentconstraint 380, and an IR Drop constraint 390. The Distance constraint370 has a constraint parameter 373 with the value 5, which indicatesthat the desired distance between the associated design objects P11 374and N10 376 is 5 distance units. The Alignment constraint 380 has aconstraint parameter 383 with the value side=edge, which indicates thatthe alignment of the associated design objects is to be determined bythe edges of the objects. The IR Drop constraint 390 has a constraintparameter 393 with the value 36, which indicates that the voltage dropbetween the associated design objects is 36 voltage units. A “T” icon325 displayed adjacent to a name 368 of the Match template instance 326indicates that the Match template instance 326 is an instance of thetemplate type T 312. The highlighted display state of the name 368indicates that the Match template instance 326 is a selected templateinstance, i.e., has been placed in a selected state by the user. Thedesign objects associated with the selected template instance arehighlighted in the design canvas 302. For example, since the designobjects P11 304 and N10 306 are associated with the Match templateinstance 326, and the Match template instance is selected, the designobjects P11 304 and N10 306 are highlighted using thicker lines thanother design objects on the canvas 302.

FIG. 4 is an illustrative drawing of a process for generating a templateinstance in accordance with some embodiments of the invention. Theprocess of FIG. 4 corresponds to the template instance generator 122 andis invoked by the template manager 120 of FIG. 1A when a new templateinstance is to be created, e.g., when a user selects a template typeicon such as the T icon 312 in the user interface 300 of FIG. 3A. Theprocess creates a template instance for a given template type, a givenset of design objects, and a given set of template instance parameters.The process begins at block 402 by determining if the given templatetype exists in a list of template types. If the template type does notexist, then the process ends by returning a failure status at block 416.If the template type does exist, then block 404 determines if there isan instance generation sub-process associated with the template type. Ifthere is no such sub-process, then the process ends by returning afailure status at block 416. If there is an instance generationsub-process, then block 406 invokes, i.e., calls, the instancegeneration sub-process with the design objects and template instanceparameters as input parameters for the sub-process. The instancegeneration sub-process may create a constraint set, or may return anempty set. Block 410 determines if the instance generation processcreated an empty constraint set, and if so, the process ends byreturning failure at block 416. If the constraint set is not empty,block 412 creates a template instance, e.g., an object in a computerprogramming language, and associates the constraint set, the parameters,and the design objects with the template instance, e.g., by settingcorresponding data members of the object to reference the constraintset, the parameters, and the design objects. The process then ends byreturning success at block 414.

FIG. 5 is an illustrative drawing of a process for validating a templateinstance in accordance with some embodiments of the invention. In oneaspect, the validation process is invoked in response to events thatcould cause the template instance to become invalid. These eventsinclude changes to parameters and reading in of the template instancefrom a file. The validation process of FIG. 5 corresponds to a portionof the template instance validator124 and is invoked by the templatemanager 120 of FIG. 1A if constraint parameters or template parameterschange, because changes to the parameters can cause the templateinstance to become invalid. The validation process of FIG. 5 is alsoinvoked if a template instance is read in from a file, because changesto the template instance made outside of the EDA tool can cause thetemplate instance to become invalid. The file may be stored onpersistent storage media such as a magnetic disk drive, an opticaldrive, random access memory, or flash memory. In other examples, thevalidation process may be invoked in response to other events such aschanges to the circuit design, e.g., when a design object is added,deleted, or modified

The validation process of FIG. 5 invokes a template instance validationsub-process to validate a given template instance. The validationprocess begins at block 502 by determining if a template type for thegiven template instance exists in a list of template types. If thetemplate type does not exist, then block 508 marks the template instanceinvalid to prevent further use of the template instance, and the processends by returning a failure status at block 522. If the template typeexists, then block 506 invokes the instance validation sub-processassociated with the template type. Block 506 passes the constraints andtemplate instance parameters associated with the template instance tothe instance validation sub-process. The instance validation sub-processis typically provided by a user, and ordinarily determines if theinstance, including the constraints, is valid according to user-definedcriteria. Next, block 510 determines if the instance validationsub-process returned a successful status. If the sub-process returned asuccessful status, then the validation process exits with a successfulstatus at block 520. Block 512 performs a recovery process. If thesub-process returned a failure status, then block 512 invokes thetemplate instance generation process of FIG. 4, starting at block 402,to re-create the template instance from the template type. The instancegeneration process then attempts to recreate a template instance,including content, e.g., constraints, and if a template instance issuccessfully recreated, returns a success status. Block 514 checks thereturn value of the instance generation process to determine if thecontent was successfully recreated. If the content was not successfullyrecreated, then block 518 deletes the template instance to preventsubsequent use of the template instance, and the process exits with afailure return status at block 522. If the content was successfullycreated, then block 516 replaces the existing content (e.g.,constraints) of the template instance with the newly created content,and the process exits with a successful return status at block 520.

FIG. 6 is an illustrative drawing of a process for validating a templateinstance in response to constraint changes in accordance with someembodiments of the invention. The validation process of FIG. 6corresponds to a portion of the template instance validator 124 and iscalled by the template manager 120 of FIG. 1A if there is a change inthe set of constraints associated with a template instance, or if thereis a change to a constraint parameter, or if there is a change in theset of design objects (i.e., a design object reference) associated witha constraint of a template instance. A template instance for which aconstraint has changed is passed to the process of FIG. 6. The processbegins at block 602 by retrieving the template type that corresponds tothe template instance by, for example, retrieving a reference to thetemplate type from the template instance. Block 604 determines if thereis an instance validation sub-process associated with the template type.If no such instance validation sub-process exists, then block 606 marksthe template instance as invalid to prevent it from being usedsubsequently, and the process ends by returning a failure status atblock 614. If an instance validation sub-process exists, then block 608invokes the instance validation sub-process by, for example, making aprocedure call. Block 608 passes the constraints and template instanceparameters associated with the template instance to the instancevalidation sub-process. The instance validation sub-process thenexecutes, and returns a success value to indicate whether the instanceis valid. Next, block 610 determines if the instance validationsub-process returned success. If the instance validation sub-processreturned success, then the validation process exits with a success valueat block 614. If the instance validator sub-process did not returnsuccess, then block 612 rejects the change to the constraints by, forexample, restoring the previous value of the constraints, and thevalidation process ends at block 614 by returning a failure status.

FIG. 7 is an illustrative drawing of a process for defining a templatetype in accordance with some embodiments of the invention. The processof defining a template type is typically performed by a user whointeracts with a template type definition interface of the EDA tool todefine the template type. The template type definition interface may bea graphical user interface, or a text-oriented command based interface,or a combination of the two.

The process of defining a template type begins at block 702 by receivinga template name, template instance creation and validation processes,and template instance parameters for the new template type. Block 704determines if a template type with the template name already exists by,for example, searching a list of template types for the template name.If a template type with the template name exists, then the process endsat block 706 by returning failure. Otherwise, block 708 creates a newobject, e.g., an object in a programming language such as Cadence®SKILL, Lisp, C++, Java™ or the like, to represent the template instance,and inserts the template name into the template type object. Blocks 710and 712 then insert references to the instance creation and validationprocesses, respectively, into the template type object. As describedabove with respect to FIG. 1A, the template instance creation andvalidation processes may be registered with the template manager 120 ofFIG. 1A through commands in an application command interface of the EDAtool using existing features of the EDA tool. Block 714 inserts thetemplate instance parameter definitions into the template instance type,and block 716 registers the template type object with the templatemanager by, for example, inserting the object into the list of templatetypes. Block 718 returns success to indicate that the template type wassuccessfully created. In one example, only parameters that match theparameter definitions created in block 714 may be used as parameters forthe template instance when the template instance is created. In thatexample, only parameters that match the parameter definitions will beaccepted as valid template instance parameters for a template instanceby the parameter list user interface feature 348 of FIG. 3A.

FIG. 8 is an illustrative drawing of a process for creating a templateinstance in an Electronic Design Automation tool user interface inaccordance with some embodiments of the invention. This process istypically executed by the EDA tool when the tool's user interfacereceives a request from a user to create a template instance The processbegins at block 802 by identifying, i.e., receiving selection of, a setof one or more design objects to be constrained. Block 804 identifies orreceives a template type to be used to constrain the objects. Block 806identifies or receives a parameter set for the template instance, andblock 808 invokes a template instance generation process, such as theprocess of FIG. 4, to create a constraint set based on the designobjects, the template type, and the parameter set. Block 810 creates thetemplate instance as, for example, an object in a computer programminglanguage. The template instance includes the constraints created inblock 808, a reference to the design objects and the parameters preparedin block 806. Block 812 ads the template instance to a list of templateinstances.

FIG. 9 is an illustrative drawing of a template instance generationsub-process in accordance with some embodiments of the invention. Thetemplate instance generation sub-process is typically a user-definedprocess, and is ordinarily invoked by the template instance generationprocess of FIG. 4. The instance generation sub-process shown in FIG. 9is an example of a user-defined sub-process and is specific toparticular types of user-defined constraints, including a MatchedParameters constraint and a Relative Orientation constraint, which arerelated to semiconductor technology. The instance generation sub-processreceives a strength parameter, which is a user-defined parameter that ismeaningful to the user and is passed from the user to the instancegeneration sub-process when a template instance is created. In oneaspect. the template instance parameters, such as the strengthparameter, are treated by the template manager as opaque, uninterpretedvalues, The MatchedParameters and Relative Orientation constraints, andthe strength parameter, are described as part of the example instancegeneration sub-process, and are necessarily present in other examples ofthe instance generation sub-process.

The instance generation sub-process begins at block 902 by retrieving astrength parameter value from the template instance for which thesub-process was invoked. The template instance may be retrieved from aninput parameter of the sub-process. Block 904 determines if the strengthparameter is equal to 1. If the strength parameter is 1, then block 906creates a Matched Parameters constraint, sets the parameters of thetemplate instance to appropriate values, block 914 returns to theinvoker a list that contains the Matched Parameters constraint, and theprocess ends. The template instance parameters may determine theconstraint list and the constraint parameters, as determined by thetemplate instance generation sub-process invoked by block 406 of FIG. 4.

If the strength parameter is 2, block 910 creates a Matched Parametersconstraint and with appropriate parameters, block 912 creates a RelativeOrientation constraint with appropriate parameters, and block 914returns to the invoker a list that contains the Matched Parameters andRelative Orientation constraints. If block 908 determines that thestrength parameter is not equal to 2, then no action is taken and thesub-process ends, although different implementations of the sub-processcould generate different constraints for subsequent strength values.

FIG. 10 is an illustrative drawing of a template instance validationsub-process in accordance with some embodiments of the invention. Thetemplate instance validation sub-process is typically a user-definedprocess, and is ordinarily invoked by the template instance validationprocesses of FIGS. 5 and 6 to determine if a template instance is valid,and, in one aspect, if the constraint set of the template instancevalid. In this example, the constraint set is considered to be invalidif the first constraint in the set is an “alignment” type constraint,and a parameter of the first constraint has the name “side” and thevalue “edge”. Any other constraint set is considered to be valid in thisexample.

The instance validation sub-process begins at block 1002 by retrievingthe template instance for which the sub-process was invoked, e.g., byretrieving the template instance from an input parameter of thesub-process. Block 1004 retrieves the first constraint from the templateinstance. Block 1006 determines if the constraint type is equal to“alignment”. If the constraint type is not equal to “alignment”, thenthe constraint set is considered to be valid, block 1014 returns asuccess value to the invoking process to indicate that the templateinstance is valid, and the sub-process ends. If the constraint type isequal to “alignment”, then block 1008 attempts to get a constraintparameter with the name “side”. Block 1010 determines if the alignmentconstraint contains a parameter with the name “side” and the value“edge”. If such a constraint is present, then the sub-process returnsfailure to indicate to the invoking process that the constraint set isinvalid. If no such constraint is present, then the sub-process returnssuccess to indicate that the constraint set is valid.

The template instance validation sub-process may also receive a changeaction parameter, which indicates the type of change action, e.g.,modification of a parameter, deletion of a constraint, modification of aconstraint parameter, or reading in of a template instance from storage.Other change action types may be added as well, e.g., an action typethat indicates the design object has changed. The user-definedvalidation process may use that action parameter when validating theconstraints.

For example, a template instance generation process could create atemplate instance with three constraints, named Matched Parameters,Alignment, and Relative Orientation, as follows:

(Template-Instance Name=Match Parameters=(Param=Value)

(constraint name=“Matched Parameters” parameters=(“1, w, m”)design-objects=(P11 N10))(constraint name=“Alignment” parameters=(side=“right” “top/left”design-objects=(P11 N10))(constraint name=“Relative Orientation” parameters=(“R0”)design-objects=(P11 N10)))

The validation sub-process shown in FIG. 10 would reject any change tothe Alignment constraint that would set the value of the “side”parameter to “edge”.

A constraint may be changed are when (1) the template instance is readin from a file, (2) a template instance parameter in edited the EDA toolUI, or (3) a constraint is edited in the user interface, i.e., aconstraint parameter or design object reference is changed in the UI. Inone aspect, changes to the design objects themselves do not trigger theconstraint observer.

In case (1) if a change to the template instance results in the “side”parameter being set to “edge” when the template instance is read in fromstorage, then the template generation process shown in FIG. 4 will beinvoked to re-create the template instance's content, thereby returningthe template instance to the state shown above. Any other changes wouldbe accepted without re-creating the constraints.

In case (2), changes to the template instance parameters do not affectthe constraint parameters, so the “side” constraint parameter cannot bemade invalid s a result of a template instance parameter change.

In case (3), if a change to a constraint or design object referenceresults in the “side” parameter being set to “edge”, then, according tothe flowchart shown in FIG. 6, the change would be rejected, i.e., notapplied to the constraint. Furthermore, each change to a constraint ordesign object reference is individually verified and rejected oraccepted. Any other changes would be accepted.

The ability to trigger the constraint validation sub-processes uponread-in of a template instance provides for the automatic repair andre-creation of constraints. Since the instance validation and generationsub-processes may be user-defined, the user can provide instructions forrepairing and re-creating the constraints in accordance with the user'stechnology or fabrication processes.

The above description is exemplary only and it will be apparent to thoseof ordinary skill in the art that numerous modifications and variationsare possible. For example, various exemplary methods and systemsdescribed herein may be used alone or in combination with various othercomputer and computer peripheral systems and methods. Additionally,particular examples have been discussed and how these examples arethought to address certain disadvantages in related art. This discussionis not meant, however, to restrict the various examples to methodsand/or systems that actually address or solve the disadvantages.

1-10. (canceled)
 11. A method of automating the validation ofconstraints associated with circuit design objects in a circuit designcreated using an electronic design automation tool, comprising:receiving notification of a change action that affects the design;identifying a template instance validation process associated with thetemplate type; invoking the validation process to validate theconstraints; receiving a validity indicator from the validation process;and if the validity indicator indicates that the constraints are notvalid, invoking a recovery process.
 12. The method of claim 11, furthercomprising: retrieving the template instance validation process from aplug-in file associated with the template type.
 13. The method of claim11, wherein the template instance validation process is provided by auser of the design automation tool.
 14. The method of claim 11, furthercomprising providing the at least one design object and a templateinstance parameter to the template instance validation process.
 15. Themethod of claim 14, wherein the template instance validation processcomprises: determining if the value of at least one constraint parameterassociated with at least one of the constraints is valid; if theconstraint parameter is valid, generating a success indicator; and ifthe constraint parameter is not valid, generating a failure indicator.16. The method of claim 11, wherein the recovery process comprises:deleting the constraints; identifying a template instance generationprocess associated with the template type; and invoking the templateinstance generation process to re-create the constraints.
 17. The methodof claim 11, wherein the change action comprises reading in of atemplate instance from a storage medium, modification of a templateinstance parameter, or a combination thereof.
 18. The method of claim11, wherein the change action comprises modification of the circuitdesign.
 19. The method of claim 11, wherein the change action comprisesa change to the at least one constraint, and the recovery processcomprises: rejecting the change action. 20-25. (canceled)
 26. A systemfor retrieving a circuit design annotated with a constraint from acircuit design file on a persistent storage medium, comprising: atemplate instance reader to retrieve a representation of a templateinstance from the circuit design file, wherein the representationincludes an instance name, a template type identifier, and at least onedesign object identifier; a template type selector to identify atemplate type specified by the template type identifier; a generatorplug-in locator to identify a template instance generator associatedwith the template type if the template type is accessible; and agenerator plug-in invoker to invoke the template instance generator tocreate a restored template instance if the instance generator isaccessible, wherein the restored template instance includes a constraintthat references at least one design object, wherein the at least onedesign object is specified by the at least one design object identifier.27-28. (canceled)
 29. A system for retrieving a circuit design annotatedwith a constraint from a circuit design file on a persistent storagemedium, comprising: a template instance reader means for retrieving arepresentation of a template instance from the circuit design file,wherein the representation includes an instance name, a template typeidentifier, and at least one design object identifier; a template typeselector means for identifying a template type specified by the templatetype identifier; a generator plug-in locator means for identifying atemplate instance generator associated with the template type if thetemplate type is accessible; and a generator plug-in invoker means forinvoking the template instance generator to create a restored templateinstance if the instance generator is accessible, wherein the restoredtemplate instance includes a constraint that references at least onedesign object, wherein the at least one design object is specified bythe at least one design object identifier. 30-31. (canceled)
 32. Acomputer program product comprising program code for automating thevalidation of constraints associated with design objects in a designcreated using an electronic design automation tool, the computer programproduct comprising: program code operable to receive notification of anchange action that affects the design; program code operable to receiveidentify a template instance validation process associated with thetemplate type; program code operable to receive invoke the validationprocess to validate the constraints; program code operable to receivinga validity indicator from the validation process; and program codeoperable to invoke a recovery process if the validity indicatorindicates that the constraints are not valid.